Semiconductor device and method of manufacturing the same

ABSTRACT

Considering further promotion of high output and miniaturization of a sensor element, it is an object of the present invention to form a plurality of elements in a limited area so that an area occupied by the element is reduced for integration. It is another object to provide a process which improves the yield of a sensor element. According to the present invention, a sensor element using an amorphous silicon film and an output amplifier circuit constituted by a thin film transistor are formed over a substrate having an insulating surface. In addition, a metal layer for protecting an exposed wire when a photoelectric conversion layer of the sensor element is patterned is provided between the photoelectric conversion layer and the wire connected to the thin film transistor.

TECHNICAL FIELD

The present invention relates to a semiconductor device having a sensorelement and a circuit comprising a thin film transistor (hereinaftercalled a TFT), and a manufacturing method thereof.

It is to be noted that a semiconductor device means any device which canfunction by utilizing semiconductor characteristics, and anelectro-optical device, a semiconductor circuit, and an electronicapparatus are all included in the semiconductor device in thisspecification.

BACKGROUND

Conventionally, as a solid-state imaging element, there has been asensor element using a single crystalline silicon substrate and a sensorelement using an amorphous silicon film.

A characteristic of the sensor element using a single crystallinesilicon substrate is that high output is achieved by forming an outputamplifier circuit over the single crystalline silicon substrate andintegrating it with the sensor element. However, the form of a completedpackaged unit is not slim since a correction filter for wavelengthsensitivity is required. In addition, the sensor element using a singlecrystalline silicon substrate has a problem in that the range ofvariations is increased by using a filter or the like.

On the other hand, a characteristic of the sensor element using anamorphous silicon film is in that a correction filter such as aninfrared light cut filter is not required since the wavelengthsensitivity is close to that of human eyes, while there is a limit sincean output value of the sensor element is not amplified. In addition, itis easily affected by noise of other signals or the like since theoutput value of the sensor element is small. The output value of thesensor element depends on the absolute amount of the sensor element(e.g., area, thickness, etc.). Therefore, in order to increase theoutput value of the sensor element using an amorphous silicon film, thearea thereof was required to be increased accordingly.

It is possible to use by amplifying the output of the sensor elementusing an amorphous film by providing an operational amplifier externallyto the sensor element using an amorphous film. In this case, however,there was another problem that the number of external parts is increasedand the sensor circuit becomes large.

The photosensitivity of the sensor element using an amorphous film islower than half of that of the sensor element using a single crystallinesilicon substrate. Therefore, there is a problem that a display devicerequiring a large area such as a liquid crystal projector is furthereasily affected by noise. Since a shield for covering a wire and thelike are necessary in order to use the sensor element using an amorphousfilm in the large display device, cost of the display device increased.

The present inventor has suggested Patent Documents 1 to 4 concerning asemiconductor device having a sensor element and a circuit comprising aTFT over a glass substrate.

[Patent Document 1] Japanese Patent Laid-Open No. Hei6-275808

[Patent Document 2] Japanese Patent Laid-Open No. 2001-320547

[Patent Document 3] Japanese Patent Laid-Open No. 2002-62856

[Patent Document 4] Japanese Patent Laid-Open No. 2002-176162

DISCLOSURE OF THE INVENTION Problems to Be Solved by the Invention

It is an object to form a plurality of elements in a limited area,reduce the area occupied by the element, and integrate the elements,considering further promotion of high output and miniaturization of asensor element.

It is another object of to provide a process which improves the yield ofa sensor element.

When each of the sensor element using a single crystalline siliconsubstrate and the sensor element using an amorphous silicon film hassmaller size, the region for mounting parts becomes smaller accordingly.Therefore, in the case of mounting by soldering, for example, it isdifficult to ensure the fixing strength. In the case where a region forfixing is small and the degree of hardness of the sensor element (whichmeans the mechanical strength of the single crystalline siliconsubstrate, the glass substrate, or the like) is high, when bendingstress is applied to the parts, the stress is not alleviated flexiblyand therefore the parts may not be fixed firmly any more because ofbalance between the fixing strength and the mechanical stress.

In view of the foregoing, it is also an object of the present inventionto achieve a sensor element having high resistance against bendingstress by using a flexible substrate as a substrate.

Means for Solving the Problems

According to the present invention, a sensor element using an amorphoussilicon film and an output amplifier circuit comprising a thin filmtransistor are integrated over a substrate having an insulating surface.Since high output can be achieved by the output amplifier circuit, alight receiving area of the sensor element can be reduced and furtherminiaturization can be achieved. In addition, since the light sensorelement and the amplifier circuit are directly connected to each otherover the same substrate, it has a characteristic that noise is noteasily superposed.

It is to be noted that the present invention in which the sensor elementusing an amorphous silicon film and the output amplifier circuitcomprising a thin film transistor are integrated has a characteristic ina connecting portion between the sensor element and the output amplifiercircuit. The characteristic is a structure in which a metal layer isprovided between a photoelectric conversion layer and a wire connectingto the thin film transistor in order to protect the exposed wire whenthe photoelectric conversion layer of the sensor element is patterned.It is to be noted that this metal layer functions as one electrode (afirst electrode) of the sensor element.

That is, after forming a wire (e.g., a source wire, a drain wire, aconnecting wire, etc.) which is electrically connected to asemiconductor layer of the thin film transistor, a metal layer is formedand patterned so as to cover the top and side surfaces of the wire.Then, a photoelectric conversion layer is formed so as to partiallycontact and overlap the wire and the metal layer. According to thepresent invention, damage to the wire due to etching of thephotoelectric conversion layer can be protected and the yield isimproved.

Furthermore, it is preferable that the wire which is electricallyconnected to the semiconductor layer of the thin film transistor isstructured by stacked layers (having two or more layers) having a metallayer using a low resistance conductive material such as aluminum as amain component, as one layer thereof.

In addition, according to the present invention, in a light receivingregion of the sensor element having a pair of electrodes, a firstelectrode is provided not to overlap the whole area of the lightreceiving region, but to overlap only a part of the light receivingregion. As a result of this, the more amount of light is absorbed in thephotoelectric conversion layer. Consequently, almost all the lightincident into the photoelectric conversion layer does not transmitthrough the metal layer (the first electrode), but transmits throughonly an interlayer insulating film, a base insulating film, and a filmsubstrate or a glass substrate to reach the photoelectric conversionlayer. It is to be noted that a second electrode which is provided so asto oppose to the first electrode is provided all over the lightreceiving region of the sensor element. In the case where thephotoelectric conversion layer has a multilayer structure including ap-type semiconductor layer or an n-type semiconductor layer as onelayer, the p-type semiconductor layer or the n-type semiconductor layeralso functions as an electrode; however, neither the p-typesemiconductor layer nor the n-type semiconductor layer is referred to asthe first electrode or the second electrode herein.

The semiconductor device of the present invention can function as alight sensor. The light incident into a diode (a photodiode) is absorbedin the photoelectric conversion layer and forms a photoelectric charge.The amount of the photoelectric charge formed by this light depends onthe amount of light absorbed in the photoelectric conversion layer. Thephotoelectric charge formed by light is amplified by the circuitcomprising a TFT and detected.

The diode used in the present invention is a Schottky diode in which aphotoelectric conversion layer is sandwiched between a first electrodeand a second electrode. It is to be noted herein that not only the diodewith the above structure but also a PIN diode, a PN diode, an avalanchediode, or the like can be used as a photoelectric conversion element forconverting light into an electrical signal.

For example, as another structure, the photoelectric conversion layersandwiched between the first electrode and the second electrode may be asingle layer which may be an i-type (intrinsic) semiconductor layer, ap-type semiconductor, or an n-type semiconductor. Alternatively, asanother structure, the photoelectric conversion layer sandwiched betweenthe first electrode and the second electrode may be two layers such asan i-type (intrinsic) semiconductor layer and an n-type semiconductorlayer; an i-type (intrinsic) semiconductor layer and a p-typesemiconductor layer; or a p-type semiconductor layer and an n-typesemiconductor layer.

It is to be noted that a PIN photodiode is structured by a pair ofelectrodes, a p-type semiconductor layer, an n-type semiconductor layer,and an i-type (intrinsic) semiconductor layer sandwiched between thep-type semiconductor layer and the n-type semiconductor layer.

A structure of the present invention disclosed in this specification isa semiconductor device mounted with a small piece of a substrate havinga light sensor element and an amplifier circuit on the same insulatingsurface. The amplifier circuit comprises an n-channel TFT having asemiconductor film having a crystalline structure. The light sensorelement includes a first electrode covering top and side surfaces of awire of the n-channel TFT, a p-type amorphous semiconductor layerpartially contacting the first electrode over the wire and the firstelectrode, an i-type semiconductor layer having an amorphous structureon the p-type amorphous semiconductor layer, an n-type amorphoussemiconductor layer on the i-type semiconductor layer, and a secondelectrode on the n-type amorphous semiconductor layer.

It is to be noted that the p-type semiconductor layer, the n-typesemiconductor layer, and the i-type (intrinsic) semiconductor layer arenot limited to an amorphous semiconductor film, and a crystallinesemiconductor film such as a microcrystalline semiconductor film (alsocalled a microcrystal semiconductor film) may be used as well.

Another structure of the present invention is a semiconductor devicemounted with a small piece of a substrate having a light sensor elementand an amplifier circuit on the same insulating surface. The amplifiercircuit comprises an n-channel TFT having a semiconductor film with acrystalline structure. The light sensor element includes a firstelectrode covering top and side surfaces of a wire of the n-channel TFT,a p-type crystalline semiconductor layer partially contacting the firstelectrode over the wire and the first electrode, an i-type semiconductorlayer having an amorphous structure on the p-type crystallinesemiconductor layer, an n-type crystalline semiconductor layer on thei-type semiconductor layer, and a second electrode on the n-typecrystalline semiconductor layer.

The contained concentration of impurities imparting n-type or p-typeconductivity can be increased by using a microcrystalline semiconductorfilm, thereby an electric resistance value of the film can be decreased.

In addition, as the p-type semiconductor layer, the n-type semiconductorlayer, and the i-type (intrinsic) semiconductor layer, a semiconductormaterial obtained by a low-pressure thermal CVD method, a plasma CVDmethod, a sputtering method, or the like, such as silicon or an alloy ofsilicon-germanium (Si_(1−X)Ge_(X)(X=0.0001˜0.02)) can be used.

It is to be noted in this specification that a crystalline semiconductorfilm is a kind of a semiconductor film having a crystalline structureand means a film having crystal grains each having a size of aboutseveral nm˜50 nm. For simplicity, a film having crystal grains eachhaving a size of more than 50 nm is referred to as a semiconductor filmhaving a crystalline structure. Further, an amorphous semiconductor filmmixed with crystal grains each having a size of about several mn˜50 nmis also referred to as a crystalline semiconductor film.

In addition, in each of the above-described structures, a p-channel TFTcan be used instead of the n-channel TFT.

In addition, in each of the above-described structures, an externalterminal provided for a chip has a two-terminal structure. Therefore,the number of pins is small similarly to that in a conventionalstand-alone amorphous visible light sensor, and sensing of visible lightcan be performed with less mounting portions.

It is to be noted in this specification that a chip provided with thelight sensor element and the amplifier circuit does not mean a chipusing a semiconductor substrate, but means a small piece of a plasticsubstrate or a glass substrate provided with the light sensor elementand the amplifier circuit.

In addition, in each of the above-described structures, the firstelectrode is a film containing Ti, and the wire of the n-channel TFT hasa three-layer structure of a first film containing Ti, a film containingaluminum, and a second film containing Ti. By employing the commonmaterial, a good ohmic contact can be obtained between the wire of then-channel TFT and the first electrode. The wire of the n-channel TFTfunctions as a source wire, a drain wire, or a connecting wire which isformed in the same step. Thus, a wire for connecting a gate electrode ofthe n-channel TFT to the first electrode also has the three-layerstructure of the first film containing Ti, the film containing aluminum,and the second film containing Ti.

Further, when the wire of the n-channel TFT has the three-layerstructure of the first film containing Ti, the film containing aluminum,and the second film containing Ti, in the case where the first filmcontaining Ti contacts the semiconductor layer, aluminum atoms can beprevented from being diffused into the channel forming region and thesecond film containing Ti prevents surface oxidation of the filmcontaining aluminum. In addition, the second film containing Ti preventsoccurrence of a protrusion such as a hillock or a whisker in the filmcontaining aluminum.

It is to be noted that the first electrode and the wire of the TFT arenot limited to Ti and another metal such as Mo may be used; and forexample, the first electrode may be a layer containing Mo and the wireof the n-channel TFT may have a three-layer structure of a first filmcontaining Mo, a film containing aluminum, and a second film containingMo.

In addition, in each of the above-described structures, the secondelectrode is patterned so as to partially overlap the first electrodeand the wire. Disconnection is prevented by partially overlapping thesecond electrode with the first electrode and the wire.

In addition, another characteristic of the present invention is that asecond electrode, a terminal electrode, or a sealing layer is formed byscreen printing in order to shorten the time for a step after aphotoelectric conversion layer is formed. It is to be noted that theelectrode (the second electrode or the terminal electrode) formed by thescreen printing is formed of a conductive material containing a resin.

In addition, in each of the above-described structures, the light sensorelement and the amplifier circuit are provided over a glass substrate ora plastic substrate.

In addition, the present invention has another characteristic that highoutput and miniaturization are achieved by forming an output amplifiercircuit comprising a TFT having a semiconductor film with a crystallinestructure (typically a polysilicon film) as an active layer and a sensorelement using an amorphous semiconductor film (typically an amorphoussilicon film) over a heat-resistant plastic film substrate that canresist the temperature in the mounting process such as solder reflowtreatment.

It is to be noted that in order to form over a plastic film substrate,an output amplifier circuit and a sensor element formed over a glasssubstrate are peeled off from the glass substrate and then transferredonto the plastic film substrate by using a peeling and transferringtechnique. Alternatively, the output amplifier circuit and the sensorelement may be formed directly over a heat-resistant plastic substratethat can resist the temperature (about 250° C.) in the mounting processsuch as solder reflow treatment. However, in the case where the outputamplifier circuit and the sensor element are formed directly over theheat-resistant plastic substrate, it is necessary to perform themanufacturing process of the output amplifier circuit and the sensorelement within the temperature range where the substrate can resist. Forexample, an HT substrate (manufactured by Nippon Steel Chemical Co.,Ltd) having a Tg of 400° C. or higher is raised as the heat-resistantplastic substrate. The HT substrate also has high transparency (atransmittance of 90% or more for a wavelength of 400 nm) and a lowthermal expansion characteristic (CTE<48 ppm).

Laser process can be performed if the sensor element is formed over aplastic substrate, thereby a minimal size can be achieved which isdifficult to be cut in the case of a single crystalline siliconsubstrate or a glass substrate.

Moreover, by using a plastic substrate, a sensor element having highresistance against bending stress can be achieved.

In addition, one of the present invention is to reduce the number ofsteps by forming a second electrode by a printing method and etching aphotoelectric conversion layer in a self-aligned manner. The presentinvention of a manufacturing method is a manufacturing method of asemiconductor device mounted with a small piece of a substrate having alight sensor element and an amplifier circuit on the same insulatingsurface. The manufacturing method of the semiconductor device ischaracterized by comprising a first step of forming a wire which isconnected to a thin film transistor constituting the amplifier circuit,a second step of forming a first electrode to cover top and sidesurfaces of the wire, a third step of stacking a first conductive typeamorphous semiconductor film, an amorphous semiconductor film, and asecond conductive type amorphous semiconductor film to cover the wireand the first electrode, a fourth step of forming a second electrode onthe second conductive type amorphous semiconductor film by a printingmethod, and a fifth step of etching the first conductive type amorphoussemiconductor film, the amorphous semiconductor film, and the secondconductive type amorphous semiconductor film in a self-aligning mannerusing the second electrode as a mask.

In addition, it is also characterized in that a sixth step of forming asealing layer to cover end portions of the first electrode and thesecond electrode by a printing method, and a seventh step of forming athird electrode on the sealing layer to contact the second electrode bya printing method are provided after the fifth step in addition to theabove-described manufacturing method.

In addition, in the above-described manufacturing method, it is alsocharacterized in that the second electrode in the fourth step is formedso as to partially overlap the wire and the first electrode.

It is to be noted that a resist mask for etching a photoelectricconversion layer may be formed by a printing method. Another structureof the present invention of a manufacturing method is a manufacturingmethod of a semiconductor device mounted with a small piece of asubstrate having a light sensor element and an amplifier circuit overthe same insulating surface. The manufacturing method of thesemiconductor device is characterized by comprising a first step offorming a wire which connects to a thin film transistor constituting theamplifier circuit, a second step of forming a first electrode to covertop and side surfaces of the wire, a third step of stacking a firstconductive type amorphous semiconductor film, an amorphous semiconductorfilm, and a second conductive type amorphous semiconductor film to coverthe wire and the first electrode, a fourth step of forming a resist maskon the second conductive type amorphous semiconductor film by a printingmethod, a fifth step of etching the first conductive type amorphoussemiconductor film, the amorphous semiconductor film, and the secondconductive type amorphous semiconductor film by using the resist mask asa mask, a sixth step of removing the resist mask, and a seventh step offorming a second electrode on the second conductive type amorphoussemiconductor film by a printing method.

In addition, it is also characterized in that an eighth step of forminga sealing layer to cover end portions of the first electrode and thesecond electrode by a printing method, and a ninth step of forming athird electrode on the sealing layer to contact the second electrode bya printing method are provided after the seventh step in addition to theabove-described manufacturing method.

In addition, in the above-described manufacturing method, it is alsocharacterized in that the second electrode in the seventh step is formedso as to partially overlap the wire and the first electrode.

In addition, according to the present invention, the sensor element andthe amplifier circuit are transferred onto a plastic film substrate byusing a peeling and transferring technique disclosed in Japanese patentLaid-Open No. 2003-174153 (a peeling method using a metal film (e.g., W,WN, Mo, etc.) and a silicon oxide film by a sputtering method). It is tobe noted that the peeling and transferring technique is not limited tothe technique disclosed in the above-described gazette and varioustechniques (e.g., a technique disclosed in Japanese patent Laid-Open No.Hei 08-288522, Hei 08-250745, or Hei 08-264796, namely a peelingtechnique for removing the peeling layer by dry etching or wet etching,etc.) may be used.

The present invention can be applied regardless of a TFT structure. Forexample, a top-gate TFT, a bottom-gate (inversely staggered) TFT, or astaggered TFT can be used. In addition, the TFT is not limited to have asingle-gate structure and a multi-gate TFT having a plurality of channelforming regions, for example, a double-gate TFT may be used.

EFFECT OF THE INVENTION

By forming a visible light sensor and an amplifier circuit comprising aTFT over the same substrate, it is possible to reduce the cost, thevolume of the parts due to reduction in thickness, and the area formounting, and besides, noise superposition can be reduced.

By forming a visible light sensor by a sensor element using an amorphoussilicon film, an infrared light cut filter is not required and thevisible light sensor can be a sensor element having a reduced outputvariation. Furthermore, output current can be increased and a variationcan be suppressed by the amplifier circuit comprising a TFT formed overthe same substrate as the visible light sensor. The light receiving areacan be reduced because of output amplification by the amplifier circuit,thereby reduction in size and weight of a mounted set, and reduction ofthe number of components can be achieved.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment modes of the present invention are described below.

Embodiment Mode 1

FIG. 1(A) is a cross-sectional view of a mounted light sensor chip ofthe present invention. FIG. 1A shows an example of a visible lightsensor chip (2.0 mm×1.5 mm) having two terminals. In FIG. 1A, referencenumeral 10 denotes a glass substrate, reference numeral 12 denotes abase insulating film, and reference numeral 13 denotes a gate insulatingfilm. Since received light passes through the glass substrate 10, thebase insulating film 12, and the gate insulating film 13, these arepreferably formed of a material having high transmittance.

A PIN photodiode 25 is structured by a first electrode 18, a secondelectrode 23, a p-type semiconductor layer 21 p, an n-type semiconductorlayer 21 n, and an i-type (intrinsic) semiconductor layer 21 isandwiched between the p-type semiconductor layer and the n-typesemiconductor layer.

A wire 19 has a stacked layer structure of a high melting point metalfilm and a low resistance metal film (e.g., an aluminum alloy, purealuminum, etc.). Herein, the wire 19 has a three-layer structure inwhich a Ti film, an Al film, and a Ti film are stacked in this order.The first electrode 18 is formed so as to cover the wire 19. Further,the second electrode 23 is provided so as to partially overlap the firstelectrode 18 with a photoelectric conversion layer structured by thep-type semiconductor layer 21 p, the n-type semiconductor layer 21 n,and the i-type semiconductor layer 21 i sandwiched therebetween.

When the photoelectric conversion layer is etched, the wire 19 isprotected by the first electrode 18 which covers it. A material of thefirst electrode 18 is preferably a conductive material whose etchingrate against an etching gas (or an etchant) of the photoelectricconversion layer is smaller than that of the photoelectric conversionlayer, and besides, the conductive material preferably does not form analloy by reacting with the photoelectric conversion layer. It is to benoted that FIG. 1A shows a case where end portions of the photoelectricconversion layer are etched to be inside end portions of the secondelectrode 23.

An amplifier circuit provided over the same substrate in order toamplify an output value of the PIN photodiode 25 is constituted by acurrent mirror circuit comprising n-channel TFTs 30 and 31. AlthoughFIG. 1A illustrates two TFTs, actually two n-channel TFTs 30 (channelsize L/W=8 μm/50 μm) and ten n-channel TFTs 31 (channel size L/W=8 μm/50μm) are provided in order to increase the output value to be five timesas large. Here, one n-channel TFT 30 and a hundred n-channel TFTs 31 areprovided in order to increase the output value to be 100 times as large.

FIG. 1B is an equivalent circuit diagram of the visible light sensorchip having two terminals. Although FIG. 1B is an equivalent circuitdiagram using an n-channel TFT, only a p-channel TFT may be used insteadof the n-channel TFT.

In order to further amplify the output value, the amplifier circuit maybe constituted by an operational amplifier (op-amp) in which ann-channel TFT or a p-channel TFT is combined arbitrarily. In this case,however, the number of terminals is five. Alternatively, by constitutingthe amplifier circuit by an operational amplifier and using a levelshifter, the number of power sources can be reduced to four terminals.

Although a case where the n-channel TFTs 30 and 31 are top-gate TFTshaving a single gate structure is shown, a double gate structure may beemployed to reduce a variation of an on-current value. Furthermore, inorder to reduce an off-current value, the n-channel TFTs 30 and 31 mayhave an LDD (Lightly Doped Drain) structure. The LDD structure is astructure in which a region with an impurity element added at lowconcentration which is referred to as an LDD region is provided betweena channel forming region and a source region or a drain region formed byadding the impurity element at high concentration. The LDD structure hasan advantageous effect of relaxing the electric field near the drain toprevent deterioration due to hot-carrier injection. Moreover, in orderto prevent lowering of the on-current value due to the hot carrier, then-channel TFTs 30 and 31 may have a GOLD (Gate-drain Overlapped LDD)structure. The GOLD structure, which is a structure in which an LDDregion is overlapped with a gate electrode with a gate insulating filminterposed therebetween, has an advantageous effect of further relaxingthe electric field near the drain than the LDD structure to preventdeterioration due to hot-carrier injection. Thus, the GOLD structure isefficient in preventing the deterioration by relaxing the electric fieldintensity near the drain to prevent the hot-carrier injection.

A wire 14 is connected to the wire 19, and extends above a channelforming region of the TFT 30 of the amplifier circuit and therefore thewire also functions as a gate electrode.

A wiring 15 is connected to the second electrode 23 and to a drain wire(also called a drain electrode) or a source wire (also called a sourceelectrode) of the TFT 31. Moreover, reference numerals 16 and 17 denoteinorganic insulating films, and reference numeral 20 denotes aconnection electrode. Since received light passes through the inorganicinsulating films 16 and 17, these are preferably formed of a materialhaving high light transmittance. It is to be noted that as the inorganicinsulating film 17, a SiO₂ film formed by a CVD method is preferablyused. When the inorganic insulating film 17 is a SiO₂ film formed by aCVD method, the fixing strength is improved.

A terminal electrode 50 is formed in the same step as that of the wires14 and 15. A terminal electrode 51 is formed in the same step as that ofthe electrodes 19 and 20.

A terminal electrode 26 is connected to the second electrode 23 and ismounted over an electrode 61 of a printed wiring board 60 by solder 64.On the other hand, a terminal electrode 53 is formed in the same step asthat of the terminal electrode 26 and is mounted over an electrode 62 ofthe printed wiring board 60 by solder 63.

Manufacturing steps for obtaining the above-described structure aredescribed below with reference to FIG. 2.

First, an element is formed over a glass substrate (the first substrate10). AN 100 is used as the glass substrate here.

Then, a silicon oxynitride film (a thickness of 100 nm) is formed as thebase insulating film 12 by a PCVD method. After that, without exposingit to the atmosphere, an amorphous silicon film containing hydrogen (athickness of 54 nm) is stacked. The base insulating film 12 may be astacked layer using a silicon oxide film, a silicon nitride film, and asilicon oxynitride film. It is to be noted that the silicon oxynitridefilm and the silicon nitride film function as a blocking layer forpreventing impurities such as an alkali metal from diffusing from theglass substrate.

Next, the above-described amorphous silicon film is crystallized by aknown technique (e.g., a solid phase crystallization method, a lasercrystallization method, a crystallization method using a catalyst metal,etc.), thereby an element using a TFT having a polysilicon film as anactive layer is formed. Herein, the polysilicon film is formed by thecrystallization method using a catalyst metal. A nickel acetate solutioncontaining nickel by 10 ppm in weight is applied by a spinner.Alternatively, a nickel element may be sprayed to the whole surface ofthe above amorphous silicon film by a sputtering method instead of thecoating method. Then, the amorphous silicon film is crystallized byperforming heating treatment to form a semiconductor film having acrystalline structure (a polysilicon layer herein). Herein, afterthermal treatment (for one hour at a temperature of 500° C.), thermaltreatment (for four hours at a temperature of 550° C.) for thecrystallization is performed to form the silicon film having thecrystalline structure.

Next, after removing an oxide film on the surface of the silicon filmhaving the crystalline structure by dilute hydrofluoric acid or thelike, laser light (XeCl: wavelength 308 nm) is irradiated in theatmosphere or an oxygen atmosphere in order to increase the degree ofcrystallinity and repair a defect left in crystal grains. Excimer laserlight having a wavelength of 400 nm or shorter, a second harmonic or athird harmonic of a YAG laser is used. Pulsed laser light having arepetition rate of about 10˜1000 Hz is irradiated and scanned on asurface of the silicon film in such a way that the laser light iscondensed by an optical system so as to have an energy density of100˜500 mJ/cm² and that the overlap rate is set at 90˜95%. Herein, therepetition rate is 30 Hz and the energy density is 470 mJ/cm² when thelaser light irradiation is performed in the atmosphere. It is to benoted that an oxide film is formed on the surface of the silicon filmbecause the laser light irradiation is performed in the atmosphere orthe oxygen atmosphere. Although description is made on the case wherethe pulsed laser is used, a continuous wave laser may be used as well.In order to obtain crystals having a large grain size, the amorphoussemiconductor film is preferably crystallized by a continuous wavesolid-state laser applying second to fourth harmonics of a fundamentalwave. Typically, a second harmonic (532 nm) or a third harmonic (355 nm)of an Nd:YVO₄ laser (the fundamental wavelength is 1064 nm) may beapplied. In the case of using the continuous wave laser, laser lightemitted from the continuous wave YVO₄ laser having an output of 10 W isconverted into the harmonic by a non-linear optical element. Theharmonic may also be emitted by setting YVO₄ crystals and a non-linearoptical element in a resonator. It is preferable to shape the laserlight into rectangular or elliptical shape on the irradiated surface byan optical system to be irradiated to a processing object. The energydensity required in this case is about 0.01˜100 MW/cm² (preferably0.1˜10 MW/cm²). Then, the laser light may be irradiated to thesemiconductor film while moving the semiconductor film relative to thelaser light at a speed of about 10˜2000 cm/s.

Subsequently, in addition to the oxide film formed by theabove-described laser light irradiation, the surface is processed usingozone water for 120 seconds to form a barrier layer constituted by anoxide film having a total thickness of 1˜5 nm. This barrier layer isformed in order to remove nickel added for the crystallization from thesilicon film. Although the barrier layer is formed using the ozone waterherein, the barrier layer may be formed by depositing an oxide filmhaving a thickness of about 1˜10 nm by a method in which the surface ofthe semiconductor film having the crystalline structure is oxidized byirradiating ultraviolet ray in an oxygen atmosphere; a method in whichthe surface of the semiconductor film having the crystalline structureis oxidized by oxygen plasma treatment; a plasma CVD method; asputtering method; a vapor deposition method, or the like. It is to benoted that the oxide film formed by the laser irradiation may be removedbefore the barrier layer is formed.

Subsequently, an amorphous silicon film containing an argon elementwhich functions as a gettering site is formed on the barrier layer witha thickness of 10˜400 nm (a thickness of 100 nm herein) by a sputteringmethod. Herein, the amorphous silicon film containing an argon elementis formed in an atmosphere containing argon using a silicon target. Inthe case where the amorphous silicon film containing an argon element isformed using a plasma CVD method, the film-forming condition is set suchthat the flow ratio of monosilane and argon (SiH₄:Ar) is 1:99, thefilm-forming pressure is 6.665 Pa (0.05 Torr), the RF power density is0.087 W/cm², and the film-forming temperature is 350° C.

After that, gettering is performed by thermal treatment for threeminutes in a furnace at a temperature of 650° C. so that the nickelconcentration in the semiconductor film having the crystalline structureis decreased. It is to be noted that a lamp annealing apparatus may beused instead of the furnace.

Next, after selectively removing the amorphous silicon film containingan argon element functioning as a gettering site by using the barrierlayer as an etching stopper, the barrier layer is selectively removed bydilute hydrofluoric acid. It is to be noted that since nickel is likelyto move to the region where the oxygen concentration is high in thegettering process, the barrier layer constituted by the oxide film ispreferably removed after the gettering.

If the semiconductor film is not crystallized using a catalyst element,the above-described steps of forming the barrier layer, forming thegettering site, performing the thermal treatment for the gettering,removing the gettering site, removing the barrier layer, and the likeare not required.

Subsequently, after a thin oxide film is formed using ozone water on asurface of the obtained silicon film having the crystalline structure(also called a polysilicon film), a resist mask is formed using a firstphoto mask, and etching treatment is performed to obtain a desired shapeso that an island-shaped semiconductor layer is formed. After theisland-shaped semiconductor layer is formed, the resist mask is removed.

Then, a small amount of an impurity element (boron or phosphorus) isadded in order to control the threshold value of the TFT if necessary.An ion doping method is performed herein in which diborane (B₂H₆) isplasma-excited without mass-separation.

Next, after removing the oxide film as well as cleaning the surface ofthe silicon film by an etchant containing hydrofluoric acid, aninsulating film containing silicon as a main component is formed as thegate insulating film 13. Herein, a silicon oxynitride film (acomposition ratio: Si=32%, O=59%, N=7%, H=2%) is formed with a thicknessof 115 nm by a plasma CVD method.

Subsequently, after forming a metal film on the gate insulating film,patterning is performed using a second photo mask to form the gateelectrode, the wires 14 and 15, and the terminal electrode 50. Then,doping is performed to the active layer to form a source region and adrain region of the TFT.

Then, after a first interlayer insulating film (not shown) constitutedby a silicon oxide film is formed with a thickness of 50 nm by a CVDmethod, a step of activating the impurity element added in eachsemiconductor layer is performed. This activation step is performed by arapid thermal annealing (RTA) method using a lamp light source, a methodin which YAG laser or excimer laser is irradiated from the back surface,thermal treatment using a furnace, or a combination of theses methods.

Next, a step of hydrogenating the semiconductor layer is performed byforming the second interlayer insulating film 16 constituted by asilicon nitride oxide film containing hydrogen and performing thermaltreatment (for 1˜12 hours at a temperature of 300˜550° C.). This processis to terminate a dangling bond in the semiconductor layer by using thehydrogen contained in the second interlayer insulating film 16. Thesemiconductor layer can be hydrogenated regardless of the existence ofthe insulating film 13 constituted by the silicon oxide film.

Subsequently, on the second interlayer insulating film 16, the thirdinterlayer insulating film 17 is formed of an insulator material. Aninsulating film having a siloxane structure formed by a coating methodor an inorganic insulating film formed by a CVD method can be used asthe third interlayer insulating film 17. Herein, a silicon oxide film isformed in order to improve adhesion.

Then, a resist mask is formed using a third photo mask and theinterlayer insulating films 16 and 17 or the gate insulating film 13 isselectively etched to form a contact hole. The resist mask is thenremoved.

Subsequently, after forming a metal stacked layer film by a sputteringmethod, a resist mask is formed using a fourth photo mask and the metalstacked layer film is selectively etched to form the wire 19, theconnection electrode 20, the terminal electrode 51, and the sourceelectrode and the drain electrode of the TFT. The resist mask is thenremoved. It is to be noted that the metal stacked layer film is astacked layer of three layers of a Ti film with a thickness of 100 nm,an Al film containing a slight amount of Si with a thickness of 350 nm,and a Ti film with a thickness of 100 nm.

Through the above-described steps, the top-gate TFTs 30 and 31 havingthe polysilicon film as the active layer are manufactured.

Next, after forming a conductive metal film (e.g., Ti, Mo, etc.) whichdoes not easily form an alloy by reacting with a photoelectricconversion layer (typically amorphous silicon) formed later, a resistmask is formed using a fifth photo mask and the conductive metal film isselectively etched to form the first electrode 18 to cover the wire 19(FIG. 2A) Used herein is a Ti film with a thickness of 200 nm formed bya sputtering method. It is to be noted that the connection electrode 20,the terminal electrode 51, the source electrode and the drain electrodeof the TFT are covered with the conductive metal film as well.Therefore, the conductive metal film also covers a side surface wherethe Al film which is the second layer of each electrode is exposed, anddiffusion of the aluminum atoms into the photoelectric conversion layercan be prevented by the conductive metal film.

A cross-sectional view at this step, of a region different from FIG. 2Ais shown in FIG. 5A. In FIG. 5A, the same portions are denoted by thesame reference numerals as in FIG. 2A. It is to be noted that the TFT isnot shown in FIG. 5A and only the wire 19 of the TFT is shown.

Subsequently, a p-type semiconductor layer, an i-type (intrinsic)semiconductor layer, and an n-type semiconductor layer are sequentiallystacked as a photoelectric conversion layer. A cross-sectional view atthis stage is shown in FIG. 5B.

As the p-type semiconductor layer, a p-type microcrystalline siliconfilm is formed with a thickness of 50 nm by a PCVD method in which theinterval between electrodes is 32 mm, the film-forming pressure is 266Pa, the RF power is 550 W, and a source gas is SiH₄(a flow rate of 4sccm), B₂H₆ (a flow rate of 20 sccm), and H₂ (a flow rate of 773 sccm).

As the i-type (intrinsic) semiconductor layer, an i-type amorphoussilicon film is formed with a thickness of 600 nm by a PCVD method inwhich the interval between electrodes is 36 mm, the film-formingpressure is 133 Pa, the RF power is 50˜88 W, and a source gas is SiH₄ (aflow rate of 100 sccm) and H₂ (a flow rate of 1000 sccm).

As the n-type semiconductor layer, an n-type microcrystalline siliconfilm is formed with a thickness of 70 nm by a PCVD method in which theinterval between electrodes is 36 mm, the film-forming pressure is 133Pa, the RF power is 300 W, and a source gas is SiH₄ (a flow rate of 5sccm), PH₃ (a flow rate of 30 sccm), and H₂ (a flow rate of 950 sccm).

Next, a metal film which is herein a Ti film with a thickness of 200 nmis formed. A cross-sectional view at this stage is shown in FIG. 5C.After that, a resist mask 90 is formed using a sixth photo mask. Across-sectional view at this stage is shown in FIG. 5D. Then, the Tifilm is etched to form the second electrode 23. A cross-sectional viewat this stage is shown in FIG. 5E. Dry etching or wet etching can beemployed; and herein, dry etching is performed using an ICP (InductivelyCoupled Plasma) etching apparatus to etch the Ti film and thephotoelectric conversion layer. A Cl₂ gas, a CF₄ gas, a CF₄ gas, an NF₃gas, or an SF₆ gas may be arbitrarily used as an etching gas.

Etching is performed for ten seconds under the first etching conditionthat a mixed gas of a Cl₂ gas (a flow rate of 40 sccm) and a CF₄ gas (aflow rate of 40 sccm) is injected, the pressure is 1.2 Pa, and an RF(13.56 MHz) electric power of 450 W is applied to the coil electrode andan RF (13.56 MHz) electric power of 100 W is applied to the substrateside (a sample stage) to generate plasma. After that, etching isperformed for eighty-eight seconds under a second etching condition thata Cl₂ gas (a flow rate of 80 sccm) is injected and the others are thesame. It is to be noted that the size of the electrode area on thesubstrate side is 12.5 cm×12.5 cm, and the size of the electrode area ofthe coil electrode (a quartz disc provided with a coil herein) is 25 cmin diameter.

Through the above-described etching, the area of the second electrode 23of one light sensor becomes 1.57 mm², which is approximately equal tothe light receiving area. In addition, through the above-describedetching, the photoelectric conversion layers (21 n, 21 i, and 21 p) areetched in a horizontal direction and formed inside an end portion of thesecond electrode by about 1.5 μm. Although the end portion of the secondelectrode is projected according to this structure, it is within a rangewhere a sealing layer can be formed at a subsequent step and thereforeit is not particularly a problem. In addition, damage due to theabove-described etching is protected by the first electrode 18 and amargin of the etching condition can be sufficiently secured by theexistence of the first electrode 18. The resist mask is then removed. Across-sectional view at this stage is shown in FIG. 5F.

Manufactured through the above-described steps is a photo diode havingthe first electrode 18, the photoelectric conversion layers 21 p, 21 i,and 21 n constituted by an amorphous silicon film or a microcrystallinesilicon film, and the second electrode 23. A cross-sectional view atthis stage is shown in FIG. 5F.

Next, a sealing layer 24 constituted by an insulator material film (aninorganic insulating film containing silicon) is formed with a thicknessof (1˜30 μm) on the whole surface to obtain a state of FIG. 2B. Herein,a SiON film is formed with a thickness of 1 μm by a CVD method as theinsulator material film. The adhesion can be improved by using theinorganic insulating film formed by the CVD method. It is to be notedthat a cross-sectional view at this step, of a region different fromFIG. 2B is shown in FIG. 6A.

FIG. 3A is a cross-sectional SEM photograph corresponding to a portionsurrounded by a chained line in FIG. 2B. A pattern diagram correspondingto FIG. 3A is shown in FIG. 3B. It is to be noted that the same portionsas those in FIG. 1 and FIG. 2 are denoted by the same reference numeralsin FIG. 3B. As shown in FIG. 3A and FIG. 3B, although the photoelectricconversion layer is formed inside due to the etching, the sealing layer24 covers it.

Subsequently, a resist mask 91 is formed using an eighth photo mask. Across-sectional view at this stage is shown in FIG. 6B. Then, theorganic insulator material film is selectively etched to form a contacthole. A cross-sectional view at this stage is shown in FIG. 6C. Theresist mask is then removed. A cross-sectional view at this stage isshown in FIG. 6D.

Then, the terminal electrodes 26 and 53 are formed by a sputteringmethod using a metal mask. Each of the terminal electrodes 26 and 53 isa stacked layer film of a Ti film (100 nm), a Ni film (300 nm), and anAu film (50 nm). The interval between the terminal electrode 26 and theterminal electrode 53 is preferably 0.3 mm or longer. The fixingstrength of the terminal electrodes 26 and 53 exceeds 5 N, which is anenough fixing strength for a terminal electrode.

Through the above-described steps, the terminal electrodes 26 and 53which can be connected by solder are formed and a structure shown inFIG. 2C can be obtained. It is to be noted that a cross-sectional viewat this step, of a region different from FIG. 2C is shown in FIG. 6D.The light sensor and the amplifier circuit can be manufactured by eightphoto masks and one metal mask, namely nine masks in total.

Subsequently, a plurality of light sensor chips is taken out by cutting.A large amount of light sensor chips (2 mm×1.5 mm) can be manufacturedfrom one large-size substrate (e.g., 600 cm×720 cm).

FIG. 4A is a cross-sectional view of one taken light sensor chip (2mm×1.5 mm), FIG. 4B is a bottom view thereof, and FIG. 4C is a top viewthereof. FIG. 4D is a photograph of the appearance of the light sensorchip seen from above. In FIG. 4, the same portions are denoted by thesame reference numerals as those in FIGS. 1 to 3. It is to be noted thatthe total thickness including the substrate 10, an element formingregion 400, and the electrodes 26 and 53 is 0.8±0.05 mm in FIG. 4A.

In order to reduce the total thickness of the light sensor chip, thesubstrate 10 may be ground to be thin by CMP treatment or the like andthen cut separately by a dicer to take out a plurality of light sensorchips.

In addition, in FIG. 4B, the size of each electrode of the terminalelectrodes 26 and 53 is 0.6 mm×1.1 mm and the interval between theelectrodes is 0.4 mm. In addition, in FIG. 4C, the area of a lightreceiving region 401 is 1.57 mm², which is approximately equal to thearea of a second electrode. In an amplifier circuit region 402, about100 TFTs are provided.

Finally, the obtained light sensor chip is mounted on a mounting surfaceof the printed wiring board 60. To connect the terminal electrodes 26and 53 to the electrodes 61 and 62, solder is formed on the electrodes61 and 62 of the printed wiring board 60 by a screen printing method orthe like in advance. Then, after the solder and the terminal electrodesare connected to each other, solder reflow treatment is performed tomount. The solder reflow treatment is, for example, performed for about10 seconds at a temperature of about 255˜265° C. in an inert gasatmosphere. Alternatively, a bump made of a metal (gold, silver, etc.),a bump made of a conductive resin, or the like may be used instead ofthe solder. Further alternatively, lead-free solder may be used formounting in consideration of an environmental problem.

FIG. 1A shows the light sensor chip mounted through the above-describedsteps. In the light sensor of the present invention (the light sensorintegrated with the circuit where an amplifier circuit for amplifyingthe output value by 100 times is provided), a photoelectric current ofabout 10 μA can be obtained at an illuminance of 100 lux. In addition,the sensitivity wavelength range of the light sensor of the presentinvention is 350˜750 nm and the peak sensitivity wavelength is 580 nm. Adark current (Vr=5 V) is 1000 pA.

Embodiment Mode 2

Described in this embodiment mode is a case where a part of the stepsdescribed in Embodiment Mode 1 is performed by screen printing. As forthe same step as that of Embodiment Mode 1, specific description thereofis omitted for simplicity.

First, a TFT, a wire 19 of the TFT, and a terminal electrode 51 areformed over a glass substrate 10 similarly to Embodiment Mode 1.

Then, similarly to Embodiment Mode 1, after a conductive metal film (Tior Mo) is formed, a resist mask is formed using a fifth photo mask andthe conductive metal film is selectively etched to form a firstelectrode 18 which covers the wire 19. It is to be noted that aconnection electrode, the terminal electrode 51, a source electrode anda drain electrode of the TFT are similarly covered with the conductivemetal film.

Subsequently, similarly to Embodiment Mode 1, a p-layer (50 nm), ai-layer (600 nm), and a n-layer (70 nm) are formed to be stacked in thisorder using a CVD apparatus, thereby a total thickness of 720 nm isobtained.

Then, a second electrode 723 is formed by a screen printing method.(FIG. 7A)

The screen printing method is a transferring method of ink or paste,which is applied onto a screen plate in which a predetermined pattern isformed of a photosensitive resin on a base made of a metal or ahigh-molecular compound fiber mesh, onto a work provided on the oppositeside of the screen plate by using a blade of rubber, plastic, or metalwhich is called a squeegee. The screen printing method has a merit inthat pattern formation in a relatively large area can be achieved at lowcost.

Herein, a screen printing machine is used and a Ni resin paste is usedas the conductive material. Alternatively, a carbon (C) resin paste maybe used as the conductive material. A printing condition is set suchthat a squeegee hardness is 900, a squeegee angle is 70°, a speed of thesqueegee stroke is 50 mm/s, a scraper speed is 250 mm/s, a clearance is1.8 mm, and a printing pressure is 0.25 MPa. It is to be noted that theclearance means an interval between the plate and the work. A heatingcondition is set at 200° C. for 30 minutes to perform hardening so thata thickness of 10±5 μm is obtained.

Subsequently, etching is performed in a self-aligned manner using thesecond electrode 723 as a mask to obtain a photoelectric conversionlayer (a p-layer 721 p, an i-layer 721 i, and an n-layer 721 n). Herein,dry etching is performed using a CF₄ gas.

Then, a sealing layer 724 is formed of a resin by a screen printingmethod. (FIG. 7B) In this step also, the screen printing machine is usedand an insulating resin paste is used as the sealing material. Aprinting condition is set such that a squeegee hardness is 90°, asqueegee angle is 60°, a speed of the squeegee stroke is 50 mm/s, ascraper speed is 250 mm/s, a clearance is 1.8 mm, and a printingpressure is 0.18 MPa. A heating condition is set at 200° C. for 30minutes to perform hardening so that a thickness of 28±5 μm is obtained.

Subsequently, third electrodes 725 and 752 are formed by a screenprinting method. In this step also, the screen printing machine is usedand the Ni resin paste or the carbon (C) resin paste is used as theconductive material. A printing condition is set such that a squeegeehardness is 90°, a squeegee angle is 70°, a speed of the squeegee strokeis 50 mm/s, a scraper speed is 250 mm/s, a clearance is 1.8 mm, and aprinting pressure is 0.25 MPa. A heating condition is set at 200° C. for30 minutes to perform hardening so that a thickness of 10±5 μm isobtained.

Then, terminal electrodes 726 and 753 are formed so as to contact andoverlap the third electrodes by a screen printing method. A copper (Cu)resin paste is used as the conductive material. A printing condition isset such that a squeegee hardness is 90°, a squeegee angle is 60°, aspeed of the squeegee stroke is 200 mm/s, a scraper speed is 250 mm/s, aclearance is 1.8 mm, and a printing pressure is 0.16 MPa. A heatingcondition is set at 160° C. for 30 minutes to perform hardening so thata thickness of 35±5 μm is obtained.

Through the above-described steps, the terminal electrodes 726 and 753that can be soldered are formed and a structure shown in FIG. 7D can beobtained. Using five masks in total, a light sensor and an amplifiercircuit can be manufactured.

Then, a plurality of light sensor chips is taken out by cuttingseparately. Finally, the obtained light sensor chip is mounted on themounting surface of the printed wiring board.

This embodiment mode can be freely combined with Embodiment Mode 1.

Embodiment Mode 3

Described in this embodiment mode is a case where a resist formation isperformed by screen printing. As for the same step as that of EmbodimentMode 1 or Embodiment Mode 2, specific description thereof is omitted forsimplicity.

First, a TFT, a wire 19 of the TFT, and a terminal electrode 51 areformed over a glass substrate 10 similarly to Embodiment Mode 1.

Then, similarly to Embodiment Mode 1, after a conductive metal film (Tior Mo) is formed, a resist mask is formed using a fifth photo mask andthe conductive metal film is selectively etched to form a firstelectrode 18 which covers the wire 19. It is to be noted that aconnection electrode, the terminal electrode 51, a source electrode anda drain electrode of the TFT are similarly covered with the conductivemetal film.

Subsequently, similarly to Embodiment Mode 1, a p-layer (50 nm), ani-layer (600 nm), and a n-layer (70 nm) are formed to be stacked in thisorder using a CVD apparatus, thereby a total thickness of 720 nm isobtained.

Then, a resist 890 is formed by a screen printing method. (FIG. 8A)Herein, a printing machine (manufactured by Micro-Tech) is used andXR1051-3 is used as the resist material. A printing condition is setsuch that a squeegee hardness is 90°, a squeegee angle is 70°, a speedof the squeegee stroke is 50 mm/s, a scraper speed is 250 mm/s, aclearance is 1.8 mm, and a printing pressure is 0.25 MPa. A heatingcondition is set at 160° C. for 30 minutes to perform hardening so thata thickness of 15±5 μm is obtained.

Subsequently, etching is performed in a self-aligned manner using theresist 890 as a mask to obtain a photoelectric conversion layer (ap-layer 821 p, an i-layer 821 i, and an n-layer 821 n). (FIG. 8B)Herein, dry etching is performed using a CF₄ gas.

The resist 890 is then removed. (FIG. 8C)

Subsequently, similarly to Embodiment Mode 2, a second electrode 823 isformed by a screen printing method (FIG. 8D). According to thisembodiment mode, unlike Embodiment Modes 1 and 2, the second electrode823 is formed after etching the photoelectric conversion layer, so thatend portions of the second electrode 823 are formed inside end portionsof the photoelectric conversion layer. In addition, according to thisembodiment mode, the second electrode is not exposed to the etching gaswhen the photoelectric conversion layer is etched so that thephotoelectric conversion layer is not formed inside from an edge of thesecond electrode, thereby good coverage at the subsequent step can beachieved.

Then, similarly to Embodiment Mode 2, a sealing layer 824 formed of aresin is formed by a screen printing method. (FIG. 8E)

Subsequently, similarly to Embodiment Mode 2, third electrodes 825 and852 are formed by a screen printing method.

Then, terminal electrodes 826 and 853 are formed so as to contact andoverlap the third electrodes by a screen printing method.

Through the above-described steps, the terminal electrodes 826 and 853that can be soldered are formed and a structure shown in FIG. 8F can beobtained. Using five masks in total, a light sensor and an amplifiercircuit can be manufactured.

Then, a plurality of light sensor chips is taken out by cuttingseparately. Finally, the obtained light sensor chip is mounted on themounting surface of the printed wiring board.

This embodiment mode can be freely combined with Embodiment Mode 1 orEmbodiment Mode 2.

Embodiment Mode 4

In this embodiment mode, description is made on a manufacturing methodin which a light sensor and an amplifier circuit formed over a glasssubstrate are peeled off the glass substrate and then transferred onto aplastic substrate.

First, a metal film 902 is formed on a glass substrate 901. A singlelayer or a stacked layer formed of an element selected from W, Ti, Ta,Mo, Cr, Nd, Fe, Ni, Co, Zr, Zn, Ru, Rh, Pd, Os, and Ir or an alloymaterial or a compound material containing the above element as a maincomponent can be used. Alternatively, a single layer or a stacked layerformed of nitride thereof such as titanium nitride, tungsten nitride,tantalum nitride, or molybdenum nitride can be used as well. Thethickness of the nitride film or the metal film 902 is 10˜200 nm,preferably 50˜75 nm.

Next, an insulating film is formed on the metal film or the nitride film902. At this time, an amorphous metal oxide film is formed between themetal film 902 and the insulating film with a thickness of about 2˜5 nm.When peeling is performed at the subsequent step, the separation occurswithin the metal oxide film, at an interface between the metal oxidefilm and the insulating film, or at an interface between the metal oxidefilm and the metal film. As the insulating film, a film is formed ofsilicon oxide, silicon oxynitride, and a metal oxide material by asputtering method. It is desirable that the thickness of the insulatingfilm be more than twice the thickness of the nitride film or the metalfilm 902, preferably 150˜200 nm.

Subsequently, a film formed of a material containing at least hydrogenis formed on the insulating film. As the film formed of a materialcontaining at least hydrogen, a semiconductor film, a nitride film, orthe like can be applied. A semiconductor film is formed in thisembodiment mode. After that, thermal treatment for diffusing thehydrogen contained in the film of a material containing at leasthydrogen is performed. This thermal treatment is performed at atemperature of 410° C. or higher, and may be performed separately from aforming process of a polysilicon film or may be performed as well as forthe forming process of a polysilicon film to reduce the number of steps.For example, in the case where an amorphous silicon film containinghydrogen is used as the material film containing hydrogen and heated toform a polysilicon film, if thermal treatment is performed at atemperature of 450° C. or higher for crystallization, diffusion ofhydrogen can be performed as well as the polysilicon film is formed.

Then, by a known technique, the polysilicon film is etched to have adesired shape so that a plurality of TFTs is formed. Each TFT has apolysilicon film including a source region, a drain region, and achannel forming region, a gate insulating film which covers thepolysilicon film, a gate electrode formed on the channel forming regionof the polysilicon film, and a source electrode and a drain electrodewhich are connected to the source region and the drain region through aninterlayer insulating film. It is to be noted that an amplifier circuitis configured by combining the plurality of TFTs.

Subsequently, a first electrode is formed which covers a wire connectedto the gate electrode of one TFT of the plurality of TFTs.

Then, a photoelectric conversion element (a light sensor) is formed soas to partially overlap the first electrode. In this embodiment mode, adiode is formed as the photoelectric conversion element. An amorphoussilicon film (or a microcrystalline silicon film) which is aphotoelectric conversion layer and a second electrode are formed on thefirst electrode. After that, the amorphous silicon film (or themicrocrystalline silicon film) and the second electrode are etched tohave a desired shape so that the diode is formed.

Subsequently, a sealing layer is formed and a terminal electrode 904 isformed. The state at this stage is shown in FIG. 9A. In FIG. 9A, a layercontaining an element covered with the sealing layer 903 is shown. It isto be noted that two terminal electrodes 904 are provided in one lightsensor and one of the terminal electrodes is connected to the secondelectrode.

Then, a fixed substrate 906 for fixing the layer containing an element903 is attached by an adhesive material 905. It is preferable that asubstrate which is more rigid than the glass substrate 901 is used asthe fixed substrate 906. In addition, an adhesive agent made of anorganic material which can be removed by an etchant is preferably usedas the adhesive material 905. Herein, a water-soluble resin is appliedas the adhesive material 905 and thereon a member with both surfacescovered with a reactive peeling type adhesive material (hereinafterreferred to as a double-sided sheet) is used.

Subsequently, the metal film 902 on the glass substrate 901 and thelayer containing an element 903 are peeled off each other by a physicalmeans. (FIG. 9B) The peeling-off occurs within the metal oxide film, atan interface between the insulating film and the metal oxide film, or atan interface between the metal oxide film and the metal film so that thelayer containing an element 903 can be peeled off the glass substratewith comparatively small force.

Then, a plastic substrate 908 a and the layer 903 containing an elementare attached to each other with an adhesive material 907 a as shown inFIG. 9C. As the plastic substrate 908 a, a synthetic resin is used. Itis preferable that a plastic substrate made of PET (polyethyleneterephthalate), PEN (polyethylene naphthalate), PES (polyether sulfone),polypropylene, polypropylene sulfide, polycarbonate, polyetherimide,polyphenylene sulfide, polyphenylene oxide, polysulfone, orpolyphthalamide is used as the plastic substrate.

As the adhesive material 907 a, various kinds of curable adhesive agentssuch as a reactive curable adhesive agent, a heat-curable adhesiveagent, a light-curable adhesive agent such as an ultraviolet ray-curableadhesive agent, and an anaerobic adhesive agent can be used.

Then, as shown in FIG. 9D, the adhesive material 905 is removed toseparate the fixed substrate 906. The adhesive material 905 is removedby heat reaction, light reaction, reaction of humidity, or chemicalreaction (e.g., water, oxygen, etc.).

Finally, division is performed by a cutter, dicing, or the like toobtain a state shown in FIG. 9E. FIG. 9E shows a case where four chipseach having a light sensor and an amplifier circuit are formed. In thismanner, a chip in which the light sensor and the amplifier circuit arefixed to a plastic substrate 908 b with an adhesive material 907 b canbe obtained.

The peeling method using a metal film and an oxide layer is appliedherein, however, the present invention is not limited to this. Forexample, the light sensor and the amplifier circuit may be peeled offthe glass substrate by a method of dissolving the glass substrate by anetchant or a method of removing the glass substrate by grinding.Alternatively, the light sensor and the amplifier circuit may be peeledoff the glass substrate by such a method that the light sensor and theamplifier circuit are formed on an amorphous silicon film (or a tungstenfilm or a tungsten oxide film) and then only the amorphous silicon film(or the tungsten film or the tungsten oxide film) is removed by anetching gas or an etchant. Further alternatively, the light sensor andthe amplifier circuit may be peeled off the glass substrate by that thelight sensor and the amplifier circuit are formed on an amorphoussilicon film containing hydrogen and then ablation is generated in theamorphous silicon film containing hydrogen by irradiating laser lightthereto.

This embodiment mode can be freely combined with Embodiment Mode 1,Embodiment Mode 2, or Embodiment Mode 3.

Embodiment Mode 5

Various electronic apparatuses can be manufactured by incorporating thelight sensor chip according to the present invention. As the electronicapparatuses, there are a video camera, a digital camera, a goggle typedisplay (a head mounted display), a projector, a monitor of a liquidcrystal television or the like, a navigation system, a sound reproducingapparatus (e.g., a car audio, an audio component system, etc.), anotebook personal computer, a game machine, a portable informationterminal (e.g., a mobile computer, a mobile phone, a mobile gamemachine, an electronic book, etc.), an image reproducing apparatusprovided with a recording medium (specifically a device which plays therecording medium such as a DVD (Digital Versatile Disc) and has adisplay for displaying the image), and the like.

This embodiment mode shows a case where the light sensor of the presentinvention is incorporated in the portable information terminal typifiedby a mobile phone or a PDA.

In recent years, power consumption of illumination such as a backlighttends to increase because information devices such as a mobile phone anda PDA has began to display various colors and the quality of a movingimage has been enhanced. On the other hand, it has been demanded toreduce the power consumption without deteriorating the display quality.Consequently, in order to reduce the power consumption, the luminance ofthe display device is controlled or the illumination of the key switchis controlled by sensing the illuminance of the environment where theinformation device is used.

FIG. 10A shows a mobile phone including a main body 2001, a housing2002, a display portion 2003, an operating key 2004, a sound outputportion 2005, a sound input portion 2006, light sensor portions 2007 and2008, and the like. The present invention can be applied to the lightsensor portions 2007 and 2008. The luminance of the display portion 2003is controlled in accordance with the illuminance obtained by the lightsensor portion 2007 or the illumination of the key switch 2004 iscontrolled in accordance with the illuminance obtained by the lightsensor portion 2008, thereby the power consumption of the mobile phonecan be suppressed.

In the case of a photographing device such as a digital camera or adigital video camera, a sensor for detecting visible light is providednear an eyepiece portion (a view window) of an optical finder and bywhich whether the photographer views the optical finder or not isdetected. For example, when the face of the photographer approaches theeyepiece portion of the finder, a shadow of the photographer covers theeyepiece portion and its vicinity. Accordingly, the detection isperformed by utilizing the change of the amount of light to be receivedby the sensor.

FIG. 10B shows a digital camera including a main body 2101, a displayportion 2102, an image receiving portion 2103, an operating key 2104, anexternal connection port 2105, a shutter 2106, a finder 2107, a lightsensor portion 2108, and the like. The present invention can be appliedto the light sensor portion 2108. Whether the photographer views theoptical finder or not is detected by the change of the amount of lightto be received by the light sensor portion 2108 provided near the finder2107. When the photographer looks through the optical finder, thedisplay portion 2102 is turned off so that power consumption can besuppressed.

In addition, the light sensor element of the present invention can beused for adjusting convergence of a projector.

In addition, when the light sensor of the present invention is mountedin a camera having no display screen (a film camera), a shutter can beoperated at the appropriate shutter speed and focus value in accordancewith the brightness obtained by the light sensor. The camera mountingthe light sensor of the present invention can prevent a failurephotograph.

This embodiment mode can be freely combined with Embodiment Mode 1,Embodiment Mode 2, Embodiment Mode 3, and Embodiment Mode 4.

INDUSTRIAL APPLICABILITY

A single crystalline silicon substrate has a limit in size and massproduction. However, by manufacturing over a glass substrate or using aplastic substrate which are inexpensive according to the presentinvention, mass production can be realized over a large-size substratewhich is, for example, a substrate having a size of 320 mm×400 mm, 370mm×470 mm, 550 mm×650 mm, 600 mm×720 mm, 680 mm×880 mm, 1000 mm×1200 mm,1100 mm×1250 mm, or 1150 mm×1300 mm. In addition, the manufacturing costper one product can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B A cross sectional view and a circuit diagram of a lightsensor device of the present invention;

FIGS. 2A to 2C Cross sectional views illustrating manufacturing steps ofa light sensor device;

FIGS. 3A and 3B An SEM photograph of a part of a light sensor device anda pattern diagram thereof;

FIGS. 4A to 4D Diagrams illustrating an outer shape of a light sensordevice of the present invention

FIGS. 5A to 5F Cross sectional process views of a light sensor device ofthe present invention illustrating Embodiment mode 1;

FIGS. 6A to 6E Cross sectional process views of a light sensor device ofthe present invention illustrating Embodiment mode 1;

FIGS. 7A to 7D Cross sectional process views of a light sensor device ofthe present invention illustrating Embodiment mode 1;

FIGS. 8A to 8F Cross sectional process views of a light sensor device ofthe present invention illustrating Embodiment mode 1;

FIGS. 9A to 9E Cross sectional process views of a light sensor device ofthe present invention illustrating Embodiment mode 1; and

FIGS. 10A and 10B Diagrams illustrating an example of electronicappliances.

1. A semiconductor device comprising: a substrate having an insulatingsurface; a light sensor element over the insulating surface, the lightsensor element comprising a first electrode, a second electrode, and aphotoelectric conversion layer; a wire electrically connected to thefirst electrode; and an amplifier circuit including an n-channel TFT,the amplifier circuit over the insulating surface, wherein the n-channelTFT includes a source electrode, a drain electrode, and a gateelectrode, wherein the gate electrode of the n-channel TFT iselectrically connected to the wire, wherein the wire is covered with thefirst electrode, wherein the second electrode is provided over thephotoelectric conversion layer, wherein end portions of the secondelectrode extend beyond end portions of the photoelectric conversionlayer, and wherein the first electrode is a film containing Ti.
 2. Asemiconductor device comprising: a substrate having an insulatingsurface; a light sensor element over the insulating surface, the lightsensor element comprising a first electrode, a second electrode, and aphotoelectric conversion layer; a wire electrically connected to thefirst electrode; and an amplifier circuit including a TFT, the amplifiercircuit over the insulating surface, wherein the TFT includes a sourceelectrode, a drain electrode, and a gate electrode, wherein the gateelectrode of the TFT is electrically connected to the wire, wherein thewire is covered with the first electrode, wherein the second electrodeis provided over the photoelectric conversion layer, wherein endportions of a top surface of the second electrode extend beyond endportions of the photoelectric conversion layer, and wherein the firstelectrode is a film containing Ti.
 3. A semiconductor device comprising:a substrate having an insulating surface; a light sensor element overthe insulating surface; and an amplifier circuit over the insulatingsurface, wherein the amplifier circuit comprises an n-channel TFT havinga semiconductor film having a crystalline structure, and wherein thelight sensor element includes a wire connected to the n-channel TFT, aphotoelectric conversion layer over the wire, and an electrode on thephotoelectric conversion layer, and an end portion of the electrodeprojects beyond an end portion of the photoelectric conversion layer. 4.A semiconductor device comprising: a small piece of a substrate havingan insulating surface; a light sensor element over the insulatingsurface; and an amplifier circuit over the insulating surface, aninterlayer insulating film over the thin film transistor; a wireconnected to the thin film transistor over the interlayer insulatingfilm; a photoelectric conversion layer formed over a part of the wire;and an electrode over the photoelectric conversion layer, wherein an endportion of the electrode projects than an end portion of thephotoelectric conversion layer.
 5. The semiconductor device according toclaim 1, wherein the photoelectric conversion layer comprises a p-typecrystalline semiconductor layer, and wherein the film containing Ti isin contact with the p-type crystalline semiconductor layer.
 6. Thesemiconductor device according to claim 2, wherein the photoelectricconversion layer comprises a P-type crystalline semiconductor layer, andwherein the film containing Ti is in contact with the p-type crystallinesemiconductor layer.
 7. The semiconductor device according to claim 1,wherein the wire has a three-layer structure of a first film containingTi, a film containing aluminum, and a second film containing Ti.
 8. Thesemiconductor device according to claim 2, wherein the wire has athree-layer structure of a first film containing Ti, a film containingaluminum, and a second film containing Ti.
 9. The semiconductor deviceaccording to claim 3, wherein the wire has a three-layer structure of afirst film containing Ti, a film containing aluminum, and a second filmcontaining Ti.
 10. The semiconductor device according to claim 4,wherein the wire has a three-layer structure of a first film containingTi, a film containing aluminum, and a second film containing Ti.
 11. Thesemiconductor device according to claim 1, wherein the second electrodeis a conductive material containing a resin.
 12. The semiconductordevice according to claim 2, wherein the second electrode is aconductive material containing a resin.
 13. The semiconductor deviceaccording to claim 3, wherein the electrode is a conductive materialcontaining a resin.
 14. The semiconductor device according to claim 4,wherein the electrode is a conductive material containing a resin. 15.The semiconductor device according to claim 1, wherein the secondelectrode partially overlaps the first electrode and the wire.
 16. Thesemiconductor device according to claim 2, wherein the second electrodepartially overlaps the first electrode and the wire.
 17. Thesemiconductor device according to claim 3, wherein the electrodepartially overlaps the wire.
 18. The semiconductor device according toclaim 4, wherein the electrode partially overlaps the wire.
 19. Thesemiconductor device according to claim 1, wherein the substrate is aglass substrate.
 20. The semiconductor device according to claim 2,wherein the substrate is a glass substrate.
 21. The semiconductor deviceaccording to claim 3, wherein the substrate is a glass substrate. 22.The semiconductor device according to claim 4, wherein the substrate isa glass substrate.
 23. The semiconductor device according to claim 1,wherein the substrate is a plastic substrate.
 24. The semiconductordevice according to claim 2, wherein the substrate is a plasticsubstrate.
 25. The semiconductor device according to claim 3, whereinthe substrate is a plastic substrate.
 26. The semiconductor deviceaccording to claim 4, wherein the substrate is a plastic substrate. 27.The semiconductor device according to claim 1, wherein an externalterminal provided over the substrate has a two-terminal structure. 28.The semiconductor device according to claim 2, wherein an externalterminal provided over the substrate has a two-terminal structure. 29.The semiconductor device according to claim 3, wherein an externalterminal provided over the substrate has a two-terminal structure. 30.The semiconductor device according to claim 4, wherein an externalterminal provided over the substrate has a two-terminal structure. 31.The semiconductor device according to claim 1, wherein the semiconductordevice is selected from the group consisting of a video camera, adigital camera, a personal computer, and a portable informationterminal.
 32. The semiconductor device according to claim 2, wherein thesemiconductor device is selected from the group consisting of a videocamera, a digital camera, a personal computer, and a portableinformation terminal.
 33. The semiconductor device according to claim 3,wherein the semiconductor device is selected from the group consistingof a video camera, a digital camera, a personal computer, and a portableinformation terminal.
 34. The semiconductor device according to claim 4,wherein the semiconductor device is selected from the group consistingof a video camera, a digital camera, a personal computer, and a portableinformation terminal.